Drop-on-demand-type inkjet heads have been known as inkjet heads that make it possible to coat required amounts of inks when required, depending on input signals.
In particular, piezoelectric (piezoelectric-element-type) drop-on-demand-type inkjet heads include: ink-supply flow channels; multiple pressure chambers that are connected to the ink-supply flow channels and that have nozzles; and piezoelectric elements that apply pressures to inks filled within the pressure chambers.
FIGS. 1A and 1B show cross-sections of a general inkjet head.
The inkjet head includes: multiple nozzles 100 that discharge liquid droplets; pressure chambers 110 that communicate with the nozzles; partitions 111 that separate the pressure chambers each corresponding to the different nozzles; diaphragms 112 that form parts of the pressure chambers; piezoelectric elements 130 that cause the diaphragms 112 to oscillate; piezoelectric members 140 that support the partition 111; and common electrodes (not shown in figures) that apply voltages to the piezoelectric elements 130.
The inkjet head additionally includes a liquid inlet although such an inlet is not shown in the figures.
The piezoelectric elements 130, and the piezoelectric members 140 supporting the partitions 111 are separated from one piezoelectric member based on dicing.
With regard to the nozzles 100 possessed by the inkjet head, their diameter is from about 10 μm to about 50 μm, and about 100 to about 300 holes forming the nozzles are arranged at intervals of about 100 μm to about 500 μm.
The inkjet head configured in this manner is operated in the following way.
When a voltage is applied into an area between the common electrode (not shown in the figures) present at the backside of the piezoelectric element 130, the piezoelectric element 130 is caused to change from the state depicted in the FIG. 1A to the state depicted in the FIG. 1B.
When the rightmost piezoelectric element 130 in FIG. 1B deforms (a bottom part of the piezoelectric element 130 deforms), a volume of the pressure chamber 110 becomes smaller, and thus, a pressure is applied to the liquid.
Due to the resulting pressure, the ink present inside the pressure chamber 110 is discharged to the outside as a liquid droplet 150.
Furthermore, in a type of inkjet head that circulates an ink therein, the inkjet head is provided with a liquid inlet, and a liquid outlet, and thus, the ink is discharged while it is circulated therein.
Advantages obtained by circulation of the ink will be described below.
The ink present in the vicinity of the nozzle is constantly in contact with the atmosphere.
Since the contact area is very small, evaporation of a solvent in the ink is intolerable.
When the solvent in the ink is evaporated, a solid content concentration of the ink will be increased, and thus, a viscosity of the ink will be raised. This may impede normal discharge of the ink.
However, if the ink is circulated to the vicinity of the nozzle, the ink with increased viscosity can constantly be replaced with fresh ink. As a result, the discharged ink in the vicinity of the nozzle always has normal ink viscosity.
Accordingly, nozzle congestion can be suppressed, and thus, constant normal discharge of the ink can be realized.
The inkjet head may have a structure based on a film-type piezoelectric element.
FIGS. 2A and 2B are diagrams that show structures of such a film-type inkjet head.
In FIG. 2A, anozzle 200 discharging a liquid, apressure chamber 210 leading to the nozzle, and a common pressure chamber 230 supplying a liquid to the pressure chamber are communicated with each other.
A film-type piezoelectric element 220 is configured on a diaphragm 212 that forms a part of the pressure chamber.
The inkjet head configured in this manner is operated in the following way.
When a voltage is applied to the film-type piezoelectric element 220, a shape of the film-type piezoelectric element 220 is changed from a state depicted in FIG. 2A to a state depicted in FIG. 2B.
When the film-type piezoelectric element 220 is deformed, a volume of the pressure chamber 210 becomes smaller, and a pressure can be conveyed to the liquid.
Based on the pressure, the liquid droplet 150 is discharged from the nozzle.
In the inkjet head having such a flow channel structure, when one piezoelectric film is driven to discharge the ink from the nozzle, a flow of the ink caused in the process of discharge influences other nozzles that are communicated with the same flow channel through a common flow channel, and a phenomenon called “crosstalk” in which the ink discharge becomes unstable will be caused.
FIG. 3 shows a cross-section view of an inkjet head disclosed in JP-A-2012-11653.
In order to cope with the problem of crosstalk, JP-A-2012-11653 discloses the following structure in an inkjet head including multiple nozzles 500 that discharge liquid droplets, multiple pressure chambers 501 provided corresponding to the multiple nozzle 500, and multiple energy-generating elements 502 applying discharge forces to the liquids inside the pressure chambers. That is, in the inkjet head, common flow channels 503 supplying liquids to the multiple pressure chambers 501, and throttle parts 504 provided in parts of flow channels each connecting between the pressure chambers and the common flow channels 503 are provided.
When pressure waves caused in the pressure chambers 501 pass through the throttle part 504, the pressure waves decay, and thus, are hardly transmitted to pressure chambers 501 for the other nozzles, thereby alleviating crosstalk.